The City Centre is the heart of Vancouver's downtown and contains the city's Financial District, the Granville Entertainment district, and many of its hotels, clubs and historical buildings. For the visitor, it's a good base from which to explore Vancouver because of its easy access to public transit, shops and restaurants. And if you want to sample Vancouver's cuisine or nightlife, or take in the mountains and harbour, it's a great place to be.
The City Centre is the destination for most transit users, so it's not much of a stretch to say all roads, buses and trains lead here. Waterfront Station is the main hub (Cordova, at the foot of Granville St), with the Skytrain, Seabus and many bus routes terminating there. A large number of buses also pickup outside Burrard Station (corner of Burrard & Dunsmuir Sts).